The present invention relates to an uninterruptible power supply apparatus for supplying electricity to a load, through converting DC electric power, which is stored or accumulated within a battery in advance, into AC electric power by means of power conversion equipment, even when interruption occurs on a commercial electric power source, and in particular, it relates to an uninterruptible power supply apparatus of a type of constant inverter power supply method.
Conventionally, the uninterruptible power supply apparatus is provided for load equipments, which must be always supplied with stable AC power, without any interruption thereof even for a moment, such as, a computer, etc., for example, for the purpose of protecting such loads from abnormality of the commercial power source, including an interruption; i.e., fluctuation on an input of the commercial power supply. For this reason, a mission of the uninterruptible power supply apparatus comes to be large, in particular, as being an apparatus for supporting a highly information-oriented society in recent years.
Further, as such the uninterruptible power supply apparatus, there are already known the following two (2) methods; i.e., so-called a constant commercial power supply method, in which the DC power is converted into the AC power through starting an inverter when an interruption occurs or voltage of the commercial power input comes down, while the commercial power input is outputted as it is when the commercial power source is in normal conditions, thereby supplying electricity to the loads, continuously, and so-called a constant inverter power supply method, in which a rectifier and an inverter provided on an input side are always operating, to convert the AC input power into the DC power, being connected with a battery circuit through a DC circuit, and further the DC power is converted into a stable AC power. The former, as is already known in the following Patent Document 1, for example, since it provides the commercial input as an output power, as it is, when the commercial power source is stable in the condition thereof, then it can be manufactured to be relatively small and light in the sizes etc., and further cheaply, however on the other hand, since the output of the apparatus also fluctuates depending upon the fluctuation of the input, when the fluctuation on the commercial power source is relatively large; therefore, it has a drawback, in particular, the stability of an output thereof.
On the contrary thereto, with the uninterruptible power supply apparatus of the latter, i.e., of the constant inverter power supply method, as is already known in the following Patent Document 2, for example, since the inverter is always operating, therefore there is no problem in the stability of the output thereof, however since the power converters (i.e., the rectifier and the inverter) are always operating, the loss in the apparatus comes to be large, an efficiency of the apparatus is deteriorated, and it is further disadvantageous, also in an aspect of noises due to a cooling fan for discharging heat generated therein. Moreover, with the uninterruptible power supply apparatus of such the constant inverter power supply method, it is also disadvantageous (i.e., being large, heavy and expensive), in aspects of an outer configuration, mass and prices thereof, comparing to those of the constant commercial power supply method mentioned above. For this reason, it is urgently necessary, for the uninterruptible power supply apparatus of such the constant inverter power supply method, to be small in the sizes, light in the weight, and further to be low in the price thereof.
Further, the uninterruptible power supply apparatus of such the constant inverter power supply method comprises, in general, a power converter built up with a rectifier, which is connected to an AC commercial power source, for converting the commercial AC power into the DC power, a reverse power converter (i.e., an inverter) for converting the DC power into the desired AC power to be supplied to the loads, and a battery connected between those power converters. And, for detecting an interruption of the AC power inputted from the AC commercial power source, normally there is an interruption detecting circuit (such as, an input voltage determining circuit) inputting the voltage thereof. Furthermore, in addition to those mentioned above, there is provided a frequency detecting circuit for detecting a frequency of the commercial AC power inputted. And, within the uninterruptible power supply apparatus in relation to such the conventional arts as were mentioned above, while the interruption detection circuit always watches or detects the voltage of the commercial AC power inputted, and a controller portion determines or detects the interruption due to a decrease of the value down to a predetermined value (for example, down to 90% of the normal voltage), thereby exchanging the apparatus into a mode when interruption occurs (i.e., an interruption mode).
Patent Document 1: Japanese Patent Laying-Open No. Hei 5-260684 (1993); and
Patent Document 2: Japanese Patent Laying-Open No. 2000-139040 (2000).
By the way, troubles on the commercial power source include a momentary voltage drop, as well as, the interruption, etc. This momentary voltage drop is a phenomenon of lowering on voltage, which is generated for a short time, about 0.07 to 2 seconds, for example, when an accident or a damage occurs on a power-transmission line or cable due to the falling of a thunderbolt. On the other hand, the interruption is generated due to a reason of stoppage of power transmission since the damaged circuit is opened for protecting a power-transmission system, or an unprepared opening of a breaker at a power distribution facility or station. However, with such the conventional uninterruptible power supply apparatuses mentioned above, not only the interruption of the power, but also the momentary voltage drop, including as well, if any abnormality occurs on voltage of the AC input (for example, down to 90% of the normal voltage), it is determined to be the interrupt, thereby starting a battery operation. Thus, while detecting the voltage (or the frequency) of the commercial AC power inputted, and when the detected value comes out a standard value, then it is determined to be the interruption, to start the operation of the battery. For this reason, even in a case of the momentary voltage drop for a short time-period, if the value of detected voltage comes out the standard value, then the operation is started upon the battery.
In more details thereof, an averaged number of the whole country (Japan) of occurring the momentary voltage drops (i.e., voltage drop of 10% or more) per one (1) consumer is 12 times/year, but on the contrary thereto, the averaged number of the whole country (Japan) of actually occurring the interruption is only 0.5 time/year; however, with the conventional uninterruptible power supply apparatus, if that momentary voltage drop comes down to be 10% or more, then the operation is changed into the battery operation. For this reason, i. e., the uninterruptible power supply apparatus is changed into the battery operation, not only when the interruption occurs actually, but also when the momentary voltage drop occurs; then, the number of times of conducting the battery operation per year comes to be large, and also the time-period thereof to be long. Also, even when an abnormality occurs on the commercial power source even one (1) time, an amount of discharge of the battery is large.
In this manner, according to the conventional arts, the apparatus conducts the battery operation, unnecessarily, even when the momentary voltage drop occurs, therefore, it gives ill influences upon a lifetime of the battery, and depending upon the cases, it needs a maintenance process, such as, checking on a location of the interruption in the power-transmission system, and further it may be causes to be large in the sizes, heavy in the weight, and expensive in the prices of the apparatus.